Compositions for the currentless deposition of ternary materials for use in the semiconductor industry

ABSTRACT

The present invention relates to the use of ternary nickel-containing metal alloys of the NiMR type (where M=Mo, W, Re or Cr, and R=B or P) deposited by an electroless process in semiconductor technology. In particular, the present invention relates to the use of these deposited ternary nickel-containing metal alloys as barrier material or as selective encapsulation material for preventing the diffusion and electromigration of copper in semiconductor components.

This application is a divisional of U.S. Ser. No. 10/555,326, now U.S.Pat. No. 7,850,770, filed Nov. 3, 2005. U.S. Ser. No. 10/555,326 is aNational Stage filing of PCT/EP04/04268, filed Apr. 22, 2004. Priorityto German application 103 21 113.6 filed May 9, 2003 and Germanapplication 103 47 809.4 filed Oct. 10, 2003 is claimed.

The present invention relates to the use of ternary nickel-containingmetal alloys of the NiMR type (where M=Mo, W, Re or Cr, and R=B or P),deposited by an electroless process, in semiconductor technology asbarrier material or as selective encapsulation material. In particular,the present invention relates to a process for the production ofternary, nickel-containing metal-alloy layers by electroless depositionon semiconductor components, where they serve as barrier material or asselective encapsulation material for preventing the diffusion andelectromigration of Cu.

PRIOR ART

Increasing interconnect density and speed requirements ofmicro-electronic components have resulted in the conductor trackinterconnect material being changed from conventional aluminium (alloys)to copper (Cu). The use of copper results in low electrical resistanceand higher stability during electromigration, but at the expense of anincrease in the overall resistance of the conductor tracks resultingfrom increasing interconnect density.

However, the use of Cu as interconnect material requires the use ofso-called diffusion barriers due to its high diffusion activity into thesubstrate (silicon) or into insulating materials (for example SiO₂).These diffusion barriers are employed beneath the Cu interconnect forprotection of the insulating material and for adhesion promotion betweeninsulating layer and interconnect layer.

The high cycle frequencies during operation of these components cause anincrease in the current densities, which can result in materialseparation of the electrical conductor material in the interconnects.This phenomenon, which is known as electromigration, results in highmortality of the components, which greatly impairs their performance.

The higher melting point of copper compared with aluminium enables animprovement in the current conduction properties of the conductortracks, which results in increased resistance to electromigrationfailure.

The life and electromigration stability are dependent principally onpossible material transport and exchange effects at thecopper/insulating material interface and not on the arrangement of thecrystal planes and the nature of the grain boundaries of the copperitself. The quality of the interfaces is therefore crucial with respectto material exchange.

It is known that the admixing (alloying) of further high-melting metals,such as, for example, refractory metals, further increases thisstability. Improved electromigration behaviour can be achieved throughthe use of thin metallic layers in combination with copper.

These electrically conductive alloy layers simultaneously also functionas diffusion barriers, which prevent the diffusion of Cu species andcharge carriers. This barrier action is caused firstly by themorphological nature of the ternary alloys through the admixing ofnonmetallic components, such as, for example, phosphorus, and secondlyby blocking of the preferred diffusion paths along the grain boundarieswithin the alloy through the incorporation of foreign atoms.

A standard process for the production of components with copperinterconnects is the so-called damascene method. In this, firstly thestructures, such as conductor track trenches and contact holes, areformed in the insulating layer by lithographic processes and subsequentdry-etching processes. A diffusion barrier and an electrical contactinglayer are subsequently applied to the conductor track structures bysputtering (PVD) or chemical vapour deposition (CVD) and filled bycopper plating. Materials frequently employed for the production ofdiffusion barriers are tantalum, tantalum nitrides, titanium, titaniumnitrides, tungsten and tungsten nitrides, etc. The electrical contactlayer used is a thin layer of copper. Chemical-mechanical polishing isused to planarise the excess interconnect material.

With increasing aspect ratio (depth to width ratio of the conductortrack structures), ever-thinner diffusion barriers have to be depositedin the conductor track trenches and contact holes. It is thereforebecoming increasingly difficult to achieve a uniformly depositedthin-film layer of the barriers by methods such as PVD and CVD.

In addition, it is known that electromigration effects occur principallyat the surface of Cu interconnects. This is due to the chemicallymodified surface structure of the copper, caused by attack during CMPand by oxidation processes.

The copper interconnects are generally built up on several levels. Sincea barrier layer for the prevention of copper diffusion is not present onthe surface of Cu, it is necessary to form a barrier layer, usually fromnon-conductive (dielectric) materials, such as silicon carbide (SiC) orsilicon nitride (SiN), before the subsequent interconnect layer isdeposited.

These dielectric materials, such as SiC or SiN, have a higher dielectricconstant than SiO₂ and are applied over the entire surface of theconductor track structures by the current process. This ultimatelyresults in an increase in the overall resistance of the semiconductorcomponent, and it is thus advantageous to coat the surface of the copperinterconnect material selectively by CMP.

Comparison of Methods

U.S. Pat. No. 4,019,910 describes mixtures and production methods forthe deposition of nickel-containing ternary alloys. U.S. Pat. No.5,695,810 claims a method for the electroless deposition of CoWP/metalbarrier layers for use in the semiconductor industry. US PatentApplication 2002/0098681 A1 furthermore describes the electrolessdeposition of ternary diffusion barriers and CoWB, CoMoB, CoWP or CoSnPencapsulation layers for improving the electromigration stability ofnovel integrated circuits with copper interconnects.

A device for electroless deposition and an autocatalytic electroplatingmethod for similar ternary alloys consisting of nickel, cobalt, tungstenand molybdenum are described in US Application 2002/0036143 A1.

Amorphous ternary alloys of the CoWB, CoMoB and CoReB type andP-containing homologues thereof are claimed in U.S. Pat. No. 6,528,409B1 for use for sealing the pores of special porous insulating materialsintegrated with copper interconnects.

JP-A 2002-93747 describes an electrically conductive structureconsisting of CoWP, CoMoP, NiWP or NiMoP having a molybdenum content inan amount in the range from 0.2 to 2 atom-% by weight, and theproduction thereof, a component and the production thereof.

OBJECT

It is therefore an object of the present invention to providecompositions for the electroless deposition of an electricallyconductive structure and a method for the production of this structure,including cleaning and activation steps, which enables structures to bedeposited, after catalytic activation, on dielectrics (for example SiO₂,SiOC, SiN or SiC) or directly on the copper interconnect in a simple andinexpensive process, precisely structures which serve as barrier layerfor preventing the diffusion of copper applied as interconnect material.

It is a further object of the present invention to provide suitableadditives for uniform layer growth of the barriers, which simultaneouslyenables an extension of the bath service life of the electrolessdeposition baths in order to prevent spontaneous chemical decompositiondue to the presence of reducing agents in aqueous solution.

The object is achieved by a process according to claim 1 and by aprocess in its particular embodiment according to claims 2 to 10. Theobject is also achieved by ternary nickel-containing metal alloys of theNiMR type (where M=Mo, W, Re or Cr, and R=B or P) deposited by anelectroless process as barrier layer or as selective encapsulationmaterial for preventing the diffusion and electromigration of Cu onsemiconductor components, produced by a process according to Claims1-10.

The present invention thus also relates to a composition for theelectroless deposition of ternary nickel-containing metal alloys of theNiMR type (where M=Mo, W, Re or Cr, and R=B or P), which composition canbe employed in a process according to Claims 1-10 and which comprisesNiSO₄×6H₂O, Na₂WO₄, Na₂MoO₄, KReO₄, NaH₂PO₂ or CoSO₄×7H₂O in aqueoussolution in a suitable concentration and optionally further additives.Compositions according to the invention have, in particular, a pH in therange 4.5-9.0. If desired, these compositions may comprise additivesselected from the group consisting of Na₃C₆H₅O₇×2H₂O, C₄H₆O₄,Na₂C₄H₄O₄×6H₂O, 2,2-bipyridines, thiodiacetic acid, dithiodiacetic acid,Triton X-114, Brij 58, dimethylaminoborane (DMAB), Na₂C₂H₃O₂, C₃H₆O₃(90%), NH₄SO₄ and RE610 (RE610: sodium polyoxyethylene) phenyl etherphosphate).

The introduction of alternative materials for the conductor trackinterconnects and novel process steps represent a crucial condition forbeing able to achieve high signal transmission speeds in the chip, evenin component structures of reduced size. The unavoidable use ofdiffusion barriers in the manufacturing process of copper multilevelinterconnects with simultaneous integration of porous insulatingmaterials enables a multiplicity of fundamental problems to be solved.This relates to the choice of the barrier materials themselves, but alsoto the choice of the electroless (autocatalytic) deposition process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a diagrammatic representation of a conventional method;

FIG. 1B shows a combined diffusion and barrier layer according to anembodiment of the disclosure:

FIG. 2 shows a diagrammatic representation of a selective encapsulationprocess of the disclosure;

FIG. 3 shows the effect of the concentration of sodium molybdate on theelemental composition of NiMoP three-component thin films;

FIG. 4A shows a Cu substrate without post-CMP cleaning;

FIG. 4B shows a Cu substrate after cleaning for 2 minutes;

FIG. 4C shows a Cu substrate after cleaning for 2 minutes and Pdactivation for 10 seconds;

FIG. 5A shows Roughness as a function of the thickness;

FIG. 5B shows Roughness as a function of the deposition time;

FIG. 6A shows SEM photomicrographs of selectively encapsulated Cudamascene structures with Pd activation;

FIG. 6B shows SEM photomicrographs of selectively encapsulated Cudamascene structures without Pd activation;

FIG. 7 shows the composition of a deposited NiMoP layer of baseelectrolyte with addition of 3.75 ppm of DTDGS and 75 ppm of Brij 58.

Attempts to achieve the present object have simultaneously resulted inthe development of a novel process for cleaning and activation, forexample by Pd catalyst nuclei. The conventional dual damascenestructuring of copper conductor tracks and contact holes by theestablished method of copper electroplating (electrolysis) representsthe boundary conditions here, limiting the choice and thus theintegration of the materials and production process into thetechnological manufacturing process.

Barrier-layer thicknesses of less than 10 nm, as mentioned in the ITRSroadmap (International Technology Roadmap for Semiconductors 2002Update, Interconnect, SIA San Jose, Calif., 2002, pp. 74-78) for thenext CMOS technologies less than or equal to 90 nm, present a majorchallenge to the barrier material and the production technology withrespect to deposition of such thin layers in a homogeneous layerthickness in structures having a high aspect ratio.

The crucial factor for operational reliability of a copper interconnectis the stability of the diffusion barrier, which is intended to preventdiffusion of copper species into the adjacent insulating interlayers andinto the active transistor regions.

By specific optimisation of the composition, causing a high proportionby weight of refractory metals to be achieved in the alloys,optimisation of the morphology of the thin layers of the ternarydiffusion barriers or top layers in the requisite thickness range isalso achieved.

Cu is used as electrical conductor for the production of conductor trackstructures and is deposited on another material in this case. Fordelimiting this material from the Cu, a ternary electrically conductiveNiMR metal alloy is employed as so-called diffusion barrier. If theunderlying material is an insulator, catalytic activation takes place inorder that NiMR can be deposited by an electroless process. If theunderlying material is catalytically active and electrically conductive,for example sputtered Co metal, NiMR deposition can take place withoutprior activation. Cu for the Cu interconnect is subsequently applied byelectroplating with the aid of the NiMR barrier layer deposited in thisway functioning as cathode. This takes place directly on the barriermaterial without additional activation or application of an electricalcontacting layer or nucleation layer.

A further application of nickel-containing alloy materials of this typeconsists in selective electroless deposition of NiMR barrier layer onthe Cu conductor track structure for encapsulating the exposed Cusurface after CMP planarisation or dry-etching processes for theprevention of oxidation, induced thin-film stresses and improvedelectromigration stability. The NiMR layer growth is initiated by thesubstitution method, in which Pd catalyst nuclei (activation) aredeposited on the copper surface. This type of initiation is necessary inelectroless deposition by means of hypophosphite as reducing agent sincethe catalytic activity of copper is lower than that, for example, of Au,Ni, Pd, Co or Pt. In the conventional activation methods (reduction ofPd ions by oxidation of Sn ions, with Pd sol), it is difficult toproduce a catalyst layer selectively on the copper interconnect. Pdnuclei adhere to the entire surface, and selective electrolessdeposition is not possible. The initiation of NiMR layer growth can alsotake place directly by modification of the electroless depositionsolution by addition of a further reducing agent, such as, for example,DMAB, after prior cleaning, or deoxidation of the Cu surface.

In both applications, use of metallic diffusion barrier layers causesimproved adhesion between the copper interconnect film and the barriermaterial.

The present invention provides compositions comprising additives forstabilisation of the developed mixtures for electroless deposition, i.e.additives for stabilisation of the thermodynamically metastable state.This causes an extension of the service life of the deposition bath. Atthe same time, the addition of these additives promotes constant anduniform layer growth in the process at the same time as a reduction inthe dimensions of conductor tracks and contact holes in integratedcomponents with increasing aspect ratios.

The present invention thus relates to a novel process for the productionof an electrically conductive structure as barrier layer by electrolessdeposition on catalytically activated insulating layers, for example onSiO₂ activated with sputtered cobalt, for use as so-called combineddiffusion barrier and nucleation layer beneath Cu interconnects, and forfurther use as encapsulation barrier on the copper interconnect surface.

This novel process is, in particular, characterised in that NiReP,NiMoP, NiWP, NiReB, NiMoB, NiWB, NiRePB, NiMoPB or NiWPB alloys are usedas barrier layers.

The refractory metal fractions which increase the thermal stability ofthe barrier are present in these alloys in high atom-percentages, forexample molybdenum with up to 24 at-%, Re with up to 23 at-% andtungsten with up to 15 at-%.

The present invention relates, in particular, to a process for theelectroless deposition of a thin metal-alloy film on a surface of ametal substrate consisting of copper, where the process comprises thefollowing steps:

cleaning (deoxidation) of the copper interconnect surface, if necessarysubsequent activation of the interconnect surface, and

provision of a pre-prepared autocatalytic plating solution, and

subsequent spraying of the substrate with or dipping of the substrateinto the pre-prepared chemical plating solution.

In particular, this is a process for the electroless deposition of athin metal layer, where the metal of the thin metal-alloy film comprisesa metal selected from the group consisting of Ni, Co, Pd, Ag, Rh, Ru,Re, Pt, Sn, Pb, Mo, W and Cr, preferably from the group consisting ofCu, Ag, Co, Ni, Pd and Pt.

The process is preferably carried out using autocatalytic platingsolutions which are essentially free from surface-active substances.

However, the base solutions used can also be autocatalytic platingsolutions comprising at least one surface-active substance. If desired,additives, such as stabilisers for extending the bath service lives ofthe electroplating solutions, can be added to the solutions.

It is also possible for additives for improving the layer properties andnature of the diffusion barriers to be added to the plating solutionsused in the process.

Ammonia- and hydrofluoric acid-free mixtures can advantageously beemployed in the process for the cleaning and activation of the Cuinterconnect surfaces, for example by Pd catalyst nuclei.

Delimitation from the Prior Art

The aqueous, newly formulated compositions can be used for theelectroless deposition of combined diffusion barrier and nucleationlayers. The latter can take place in a single process step on use of thecompositions according to the invention. However, the compositions canalso be used for the deposition of encapsulation material on Cuinterconnects.

The method of electroless deposition is particularly suitable forselective deposition of diffusion barriers on use of so-called porousinsulating materials. It is known that conventional PVD methods and CVDprecursors penetrate the relatively mechanically unstable pores of thesematerials, it being possible for these to be partially sealed or closedduring deposition of the barrier.

The ternary alloy materials can be deposited by the process according tothe invention using the novel compositions by electroless platingmethods as very thin and efficient barrier films having a film thicknessof less than 200 Å. They thus meet the requirements for conductor trackdimensions in ultra large scale integrated (ULSI) circuits, with respectto surface nature, uniform step coverage and flank coating of theinterconnects, to a greater extent than with conventional techniques.

A particular advantage of the specific application of these electricallyconductive alloy materials as encapsulation layer consists in selectivedeposition of the barrier layers on Cu as interconnect material.

The high content of refractory metals, such as, for example, of up to 24at-% of molybdenum, advantageously gives rise to improved diffusionbarrier properties with respect to Cu diffusion.

An NiMoP alloy is a preferred material for electroless deposition on Cusince small amounts of Mo increase the thermal stability of the alloyand thus improve the diffusion resistance to copper.

The ternary barrier materials employed in accordance with the inventionfurthermore have high electrical conductivity with a low specificresistance of less than 250 μΩcm. This gives rise to a reduction in thesignal transmission delay (“RC delay”) as component structures becomesmaller.

The overall resistance of the conductor tracks and the probability offailure due to electromigration effects during operation of thecomponents are minimised compared with dielectric materials, such as SiCor SiN, or in some cases even suppressed through a suitable choice ofthe process parameters, but also by continuous process monitoring.

The use of the electrically conductive ternary barriers according to theinvention gives rise to improved interface quality with respect to thecopper/metallic diffusion barrier/insulating matrix interfaces.Diffusion of copper species and electromigration phenomena aresuppressed by an increased activation energy transition barrier at themetal/metal interface.

At the same time, the strong bond of metals to one another increases theadhesion of the barrier layer to the copper interconnect material andcontributes to more advantageous production of finer interconnects, incontrast to original dielectric materials, such as SiC or SiN.

Furthermore, the modified composition ensures an extension of the bathservice lives (stabilisation) of the electroless deposition bathsaccording to the invention. At the same time, the morphology and layergrowth of the deposited alloys are positively influenced with respect tothe barrier action.

An extension of the service life of the deposition bath results inreduced consumption of chemicals. In addition, the work involved in theproduction process is reduced, and production costs are thus alsolowered. Furthermore, the addition of additives promotes constant,uniform layer growth at the same time as a reduction in the dimensionsof conductor tracks and contact holes in integrated components withincreasing aspect ratios.

A further advantage of the present invention is to be seen in the methodof electroless deposition of ternary alloys for the production ofso-called combined diffusion barrier and nucleation layers in oneprocess step from aqueous solution.

A resultant advantage is simplification of the process sequence with theelimination of individual process steps for the production of integratedcircuits in semiconductor technology by enabling immediately subsequentelectroplating with copper from aqueous solution (FIG. 1). A completelywet-chemical process procedure in wet-chemical cluster deposition units,as usually employed in the semiconductor industry, is thus possible(FIG. 1).

Copper is electroplated for interconnection on the ternary metal barrierlayer as cathodic contacting. After the excess electrolyticallydeposited copper, which is located over the contact holes andinterconnect trenches, has been removed, for example bychemical/mechanical polishing (CMP), the copper surface is cleaned.Catalyst nuclei can subsequently be deposited on the copper surface withthe aid of a Pd-con-taining mixture by ion plating (“cementation”,electrochemical deposition by charge exchange). This type ofelectrochemical charge exchange is not possible on the insulating layer.The catalyst nuclei thus subsequently enable selective electrolessdeposition of, for example, NiMoP only on the Cu interconnect, asdescribed in the following working examples (FIG. 2) where referencenumeral (1) corresponds with the diffusion layer, reference numeral (2)corresponds with the nucleation layer, reference numeral (3) correspondswith the catalytically activated insulating layer, reference numeral (4)corresponds with the copper interconnect and reference numeral (5)corresponds with the encapsulation barrier.

Variation Ranges of the Process Parameters, Including Preferred Rangesand Values

Preferred concentration ranges are shown in the following tables.

TABLE 1 Compositions of electroless plating solutions and processparameters for the deposition of ternary NiP alloys CompositionConcentration [mol/l] Operating conditions NiWP NiMoP NiReP NiSO₄ × 6H₂O 0.02-0.1  0.02-0.1  0.03-0.1  Na₂WO₄   0-0.14 — — Na₂MoO₄ — 0-3 ×10⁻² — KReO₄ — —    0-1 × 10⁻² NaH₂PO₂ 0.1-0.5 0.1-0.5 0.2-0.8 DMAB —  4× 10⁻³-1.5 × 10⁻⁴ — Na₃C₆H₅O₇ × 2 H₂O 0.07-0.22 0.1-0.3 — C₄H₆O₄ —0.03-0.3  0.03-0.2  Na₂C₄H₄O₄ × 6 H₂O — — 0.1-0.5 2,2-Bipyridine — — 1-5 ppm Dithioacetic acid —  0-20 ppm — Triton X-114 — — 0-200 ppm Brij58 — 0-100 ppm — pH 8.2 9.0 4.5 Temperature [° C. ± 1] 60-80 60-80 60-65

TABLE 2 Compositions of electroless plating solutions and processparameters for the deposition of ternary boron-containing alloysComposition Concentration [mol/l] Operating conditions NiMoB CoReB NiSO₄× 6 H₂O 0.03-0.1  — CoSO₄ × 7 H₂O — 0.06-0.1  KReO₄ —    0-3 × 10⁻²Na₂MoO₄ 3 × 10⁻² — DMAB 0.05-0.2  0.05-0.2  Na₂C₄H₄O₄ × 6 H₂O 0.05-0.150.05-0.15 Na₂C₂H₃O₂ 0.1-0.3 0.1-0.3 C₃H₆O₃ (90%) 0.03-0.05 0.03-0.05NH₄SO₄ 0.3-0.5 0.3-0.5 2,2-Bipyridine  0-20 ppm  0-20 ppm RE610 0-200ppm 0-200 ppm pH 5.4 6.0 Temperature [° C. ± 1] 60-65 70-80Critical Limits

For NiMoP, solutions in the working examples should have pH values of 9and should not differ from this by more than ±1 since otherwise amodified alloy composition with different barrier properties results.

A buffer action is achieved by the suitable use of carboxylic acids andsalts thereof as complexing agents.

The deposition temperature should not exceed the value of max. 90° C.since otherwise spontaneous decomposition of the autocatalytic platingsolution would be the consequence. In general, increased depositiontemperatures reduce the bath stability and thus bath service lives ofthe deposition solutions.

Variation of the Process or Procedure

The present invention provides a process for the production ofelectrically conductive structures by prior cleaning and activationsteps. The cleaning sequence can optionally be extended by rinsing withalcohol, for example ethanol or isopropyl alcohol, in order to improvethe cleaning action. The cleaning can also be supported by the use of amechanical brush process (“scrubber”).

The Pd activation solution can be prepared from salts, such as palladiumchloride or palladium acetate.

The Pd activation solution can be varied by the addition of additives,for example by addition of complexing agents, such as EDTA or Quadrol(Quadrol: ethylenediamine-N,N,N′,N′-tetra-2-propanol).

The Pd activation solution can be supplemented by additives, such assurface-active substances, for example Re610 or Triton X-114, orpoly-ethylene glycols (Triton X-114: poly(oxyethylene) octyl phenylether or mono(1,1,3,3-tetramethylbutyl)phenyl)ether).

The Pd activation solution can be employed in both spraying and dippingprocesses.

The present invention formulates electroless deposition solutions foruse in spraying or immersion processes which comprise at least one firstmetal component as main alloy constituent, a complexing agent, areducing agent and a pH regulator, which sets the pH in the range from 4to 12.

In a particular embodiment of the present invention, an electrolessdeposition solution is provided which comprises a second metal componentwhich improves the barrier properties of the diffusion barrier. Inaddition to the first complexing agent, at least one further complexingagent from the group consisting of carboxylic acids and amino acids isselected.

The pH of the solutions is set to a pH in the range from 7 to 9 byaddition of a hydroxide base, such as ammonium hydroxide, sodiumhydroxide solution, potassium hydroxide solution or tetramethyl-ammoniumhydroxide (NH₄OH, NaOH, KOH or TMAH respectively).

For applications on semiconductor components, the alkali-free bases, inparticular, are preferred.

The pH can also be set to a pH in the range from 4 to 7 by the additionof a mineral acid.

Surfactants can optionally be used as additives in the broad sense.These can be both anionic (containing functional groups, such ascarboxylate, sulfate or sulfonate groups) and nonionic (for examplepoly-ether chains) surfactants.

Additives which can be used are optionally 2,2-bipyridines, thiodiaceticacid, thiodiglycolic acid, dithiodiglycolic acid, ammonium thiolactate,ammonium thioglycolate, thioborates, boric acid, thiosulfates, sodiumdithionite, borax, glycerol and hydroxyl and ammonium derivatives ofbenzene (for example 3,4,5-trihydroxybenzoic acid, hydroquinone, metol,p-phenylenediamine, Rodinal and Phenidone), both as individualcomponents and in combination with one another.

If desired, inorganic salts, such as, for example, magnesium compounds,can also be employed as additives.

Areas of Application and Uses

The present invention provides compositions for electroless depositionbaths having extended bath service lives (stabilisation of thethermodynamically metastable state). In accordance with the invention,the improved properties are achieved by the addition of suitableadditives, as enumerated above. This extension of the service livesresults in reduced consumption of chemicals and in addition reduces thework involved in the production process and thus also the costs of theresultant product. These additives also promote constant and uniformlayer growth at the same time as a reduction in the dimensions ofconductor tracks and contact holes in integrated components withincreasing aspect ratios.

For the investigation of barrier materials (with respect to compositionand microstructure), electroless deposition of ternary nickel-basedalloys on SiO₂/Si wafers sputtered with 40 Å of cobalt was carried out.The acidic metal-deposition solution, which was used, for example, inorder to deposit NiReP alloy, comprised NiSO₄×6 H₂O 0.03-0.1 M,perrhenate 0.001-0.01 M, citric acid as complexing agent, hypophosphiteas reducing agent and additives. The metal-deposition bath was operatedwithin a temperature range of from 50 to 80° C. The thickness of thebarrier layers varied between 10 and 30 nm. The encapsulating alloyfilms were analysed by four-point probe layer resistance measurements,Auger electron spectroscopy (AES), atomic force microscopy and X-raydiffraction (XRD). A study of the crystallographic structure of the thinfilms was carried out by XRD with glancing incidence. The barriereffectiveness on the silicon surface of the Cu barrier/SiO₂/Si systemswas firstly characterised by scanning electron microscopy (SEM) usingthe selective Secco etching method. For analysis of copper surfaceactivation, substrates having a layer sequence of Cu (150 nm)/TiN (10nm)/SiO₂ (500-1000 nm) were used on Si wafers. The Cu surfaces werefirstly prepared by cleaning with Inoclean 200™ post-CMP cleaningsolution and then activated with Pd ion solution. Alternatively, thisactivation was used in order to allow self-aligned NiMoP barriers togrow (Inoclean 200™: mixture of dilute carboxylic acid esters andphosphoric acid). Alternatively, this cleaning may also be carried outusing dilute HF solution, oxalic acid and other inorganic acids, forexample sulfuric acid. Direct electroless metal deposition was achievedby direct addition of dimethylaminoborane (DMAB) to the electrolessmetal-deposition bath. The selectivity was assessed by energy dispersionX-ray measurements (EDX).

The aqueous deposition solutions were designed so as to give ternaryalloys which comprise large amounts of high-melting metal component.

The elemental composition of the deposited Ni-based thin films wasinvestigated by the AES depth profiling method.

Use as Combined Diffusion Barrier and Contact Layers:

The depth profiles of these layers indicate that nickel is depositeduniformly as a function of the depth, while phosphorus tends to beconcentrated in the upper surface layer and the high-melting metals atthe barrier/SiO₂ interface. The standardised atom fractions of nickel,phosphorus and high-melting metal component of the various alloys areshown. The nickel fractions remain relatively constant at approximately60-70 at-%, while larger variations are measured for the remainingcomponents, particularly phosphorus. All ternary alloys presented herecomprise high proportions of high-melting metal, for example up to ˜23at-% for NiMoP thin films (Table 3).

During electroless deposition of polymetallic alloys frommetal-deposition solutions containing hypophosphite or aminoborane,phosphorus (or boron) is deposited at the same time in the film layer asa result of a parallel oxidation reaction of the reducing agent [6].

The influence of the experimental conditions on the composition of theternary alloy was investigated (FIG. 3). Factors which appeared toinfluence the thin-film composition were the type of high-melting metaland reducing agent used as well as the concentrations of thehigh-melting metals and complexing agents. As can be seen from theresults, co-deposition of molybdenum occurs at the expense ofphosphorus. The incorporation of large amounts of high-melting metalinto the various three-component alloy films was therefore achieved bycontrol of the respective concentrations of ions of high-melting metalin the solutions of the externally electroless deposition bath.

It has been suggested that the addition of high-melting metal improvesthe thermal stability of the deposits and the barrier properties byblocking diffusion paths along the grain boundaries [8]. The alloy wasamorphous during deposition. In fact, many of the alloy films areamorphous and metastable during deposition, with their structurechanging after post-thermal treatment.

In the case of NiMoP, a polycrystalline microstructure withmicrocrystallites embedded in an amorphous matrix has been describedusing XRD after conditioning. The resistance determined using thefour-point probe technique for thin NiMoP films with a thickness of from10 to 30 nm was determined as being in the range from 60 to 70 μΩcm.Such low resistance values are desired in order to minimise thecontribution of the barrier layer to the total interconnect conductionresistance. The influence of the content of high-melting metal andaccordingly of the co-deposited reducing-agent component and theassociated thin-film microstructure on the properties of the diffusionbarrier was investigated. The barrier effectiveness was assessed usingSecco etching. It was found that thin layers of NiMoP with a thicknessof 30 nm deposited by an electroless process were stable for 1 hour atup to 450° C.

Use for the Encapsulation of Copper Conductor Track Structures:

Regarding the use of the developed ternary alloys as metal barriers onCu inlaid structures, a number of problems had to be assessed. The mostcrucial aspect is fully selective deposition on Cu structures. Thenickel-based alloys investigated are preferred materials for avoidinglayer separation of the Cu/self-aligned barrier interface, since Nitends to form strong covalent bonds with Cu, which has a favourableeffect on the adhesion of the boundary layers. In addition, preparationof the Cu surface and the stability of the electroless metal-depositionbath represent critical problems since the latter is in a metastablethermodynamic equilibrium and tends to decompose spontaneously.Preparation of the Cu surface therefore plays a key role in thesecatalytic processes. Before electroless alloy deposition, a wet processincluding removal of copper oxide by CMP and Pd catalyst activation wasdeveloped. Firstly, acid cleaning using post-CMP cleaning solutioncontaining organic acids was carried out in order to remove copper oxideselectively. In a next step, the Cu surface was activated catalyticallyby deposition of a discontinuous Pd nucleation layer, which enabledelectroless deposition of the ternary alloy usinghypophosphite-containing metal-deposition solutions (FIG. 2).

TABLE 3 Composition of thin-film three-component alloy determined by AESdepth profile analyses. Three-com- ponent alloy M1 at-% M2 at-% R at-%NiReP ~70 8-23 14-19 NiMoP ~60 ~24  6-10 NiWP 70-75 ~15  7-19 NiMoB65-70 7-13 13-17

The effect of each step of the activated process (cleaning of thesurface, activation and deposition) was assessed with respect to surfacemorphology, surface composition and surface selectivity of the deposits.Before cleaning, CMP residues were observed (see FIG. 4 a). Afterpost-CMP cleaning for 2 minutes, these residues had been removed, withno reduction in the quality of the Cu surface (FIG. 4 b). The subsequentactivation step is very sensitive to surface cleaning, and dense Pdnucleation was achieved (FIG. 4 c).

The effect on the surface roughness after cleaning and activation wasinvestigated by AFM. The general tendency is that a longer cleaningtreatment reduces the roughness of the Cu surface. This behaviour isalso retained after activation. Pd nucleation is accompanied by surfaceroughening, which is ascribed to the deposition of isolated metal isletson the smooth Cu surface. It has been found that, of the conditionstested in this study, a cleaning treatment lasting 2 minutes givessatisfactory results. Grain growth of the deposited barrier films occursat between 10 and 60 seconds in the initial stages of the electrolessmetal-deposition process investigated. The deposits change from afine-grained structure to a morphology with a somewhat cauliflower-likestructure [9]. This observation is supported by AFM measurements, whichshow surface roughening after 30 to 60 seconds in the early depositionstages without regular development (FIG. 5 a). The barrier thickness isfound to have a linear dependence on the deposition time, and a shortdeposition (20 seconds) is adequate to achieve the desired thickness.Short deposition times make the externally electroless process veryattractive for manufacturing in which high throughputs are desired (FIG.5 b).

The selectivity of the electroless NiMoP deposition process on Cusurfaces was investigated by EDX against various non-conductive andbarrier materials, such as, for example, SiO₂, SiC, SiOC, SiN, TiN andTaN. As can be seen from SEM and EDX measurements, selectivity wassuccessfully achieved on cover substrates (Example 3). No deposition wasobserved on the other materials, apart from in the case of coppersubstrate, where the elements Cu, Ni, Mo and P were detected by EDX.Selective deposition during the developed electroless metal-depositionprocess on patterned substrates was detected. In general, optimumselectivity is achieved with short cleaning and activation times. FIG. 7a shows pictures of Cu damascene structures selectively encapsulated bythe NiMoP alloy.

In general, activation by inoculation with Pd catalyst is necessary inorder to initiate the electroless metal-deposition reaction onnon-catalytic surfaces. In addition, however, the catalyst may be apotential source of contamination for the electroless metal-depositionbath and make the latter unstable during processing owing to thetransfer of activator solution. In the case of conventional electrolessmetal deposition on Cu surfaces using hypophosphite compounds asreducing-agent component, it is not possible to achieve electrolessmetal deposition without prior Pd activation. In spite of the catalyticproperties of Cu, hypophosphite does not reduce Ni²⁺ or Co²⁺ ions on theCu surface. An electroless NiMoP deposition process on cleaned Cusubstrates by the addition of 0.02-0.06 mol/l of DMAB to themetal-deposition bath without Pd activation was investigated, andselective encapsulation of Cu conductor track structures was observed(see FIG. 7 b).

The three-component alloy films investigated, for example NiMoP, givesignificantly low resistance values and adhere well to Cu. Ultrathindeposits were achieved using an electroless deposition process. Adiffusion barrier effectiveness has been demonstrated up to 450° C. Thehigh selectivity of the electroless process makes these layersparticularly attractive for use as post-CMP encapsulation. The use ofthese films as selective metal encapsulation layers can improve theelectromigration reliability of integrated circuits made from coppercompared with non-conductive encapsulation layers, such as, for example,SiN or SiC.

The following examples, which fall within the scope of protection of thepresent invention, are given for better understanding and in order toillustrate the invention. However, they are not suitable, owing to thegeneral validity of the inventive principle described, for reducing thescope of protection of the present application only to these examples.Furthermore, the contents of the cited patent specifications should beregarded as part of the disclosure of the invention of the presentdescription.

EXAMPLE 1 Step 1 (Cleaning)

The removal of adherent copper oxides and organic copper compounds fromthe copper surface is carried out using a post-copper CMP cleaningmixture, for example CuPure™ Inoclean 200 from Merck (consisting of 2-4%of dimethyl malonate, 2-4% of 1-methoxy-2-propanol, <0.5% of methylacetate and <0.5% of phosphoric acid). The cleaning solution here can beemployed as an 80% solution or diluted as an up to 10% solution by thedipping or spraying method. If desired, a further dipping step withethanol or isopropanol can be carried out for cleaning. The alcohol canalso be added directly to the cleaning mixture in order to eliminate theprocess steps.

Experimental Conditions:

Dipping time of 2 minutes into Inoclean 200 cleaning solution (dilution10%), rinsed for 30 seconds with deionised water and not blown dry.

Spraying for 2 minutes with Inoclean 200 cleaning solution (dilution 10%and 50%), rinsed for 30 seconds with deionised water and not blown dry.

Using alcohols: dipping time of 2 minutes into Inoclean 200 cleaningsolution (dilution 10%), rinsed for 30 seconds with deionised water, for60 seconds with isopropyl alcohol and for 10 seconds with deionisedwater, and not blown dry.

Step 2 (Activation)

The Cu surface cleaned in this way is selectively activated byelectrochemical charge exchange by treatment with a Pd²⁺-containingsolution.

Composition of the Activation Solution:

-   a.) Acetic acid 5.0 mol/l-    PdCl₂1×10⁻³ mol/l-    HCl (37%, 1×10⁻⁴ mol/l-   b.) Acetic acid 5.0 mol/l-    Pd(OAc)₂1×10⁻³ mol/l-    HCl (37%), 1×10⁻³ mol/l    Experimental Conditions:

The cleaning, activation and deposition steps of NiMR should be carriedout in a sequence at very small time intervals.

The Cu surface is firstly dipped into diluted cleaning solution (10% or50%), rinsed briefly with deionised water, dipped, without blow-drying,into a Pd²⁺ solution for 10 seconds or 20 seconds and rinsed brieflywith deionised water at room temperature. Blow-drying is not carriedout.

Step 3 (Autocatalytic Deposition in Combination with Pd Activation)

The ternary metal alloy, for example NiMoP, is then deposited on the Cuinterconnect surface activated with Pd nuclei.

For this purpose, stock solutions are prepared for a base electrolyte 1.The final deposition solution used is a volume of 250 ml. The stocksolutions are mixed in the corresponding ratio.

Composition of Base Electrolyte 1:

26.29 g/l NiSO₄ × 6H₂O (0.1 mol/l) 26.47 g/l Na₃ citrate × 2H₂O (0.09mol/l)   0.24 g/l Na₂MoO₄ × 2H₂O (0.001 mol/l)  23.62 g/l succinic acid(0.2 mol/l) 21.20 g/l NaH₂PO₂ × H₂O 0.2 mol/l

Of the individual components, stock solutions are prepared whoseconcentration is selected in such a way that the solutions can be mixedwith one another in equal volume ratios and give the respective baseelectrolytes. To this end, the substances are dissolved in deionisedwater in a 1 l volumetric flask.

Stock solution K1=131.5 g/l NiSO₄×6H₂O

Stock solution K2=132.4 g/l Na₃ citrate×2H₂O

Stock solution K3=1.2 g/l Na₂MoO₄×2H₂O (for base electrolyte 1)

Stock solution K4=118.1 g/l succinic acid

Stock solution K5=106.0 g/l NaH₂PO₂×H₂O

In order to prepare the final deposition solution, firstly 50 ml ofstock solution K1 and 50 ml of stock solution K2 are combined. Inparallel, 50 ml of stock solution K3 and 50 ml of stock solution K4 arecombined. The two mixtures are subsequently combined. The pH is adjustedto a value of 9.0 using 50% NaOH solution with stirring. Stock solutionK5 is finally added.

Composition of Base Electrolyte 2:

26.29 g/l NiSO₄ × 6H₂O  0.1 mol/l 26.47 g/l Na₃ citrate × 2H₂O 0.09mol/l  0.24 g/l Na₂MoO₄ × 2H₂O 0.001 mol/l   1.18 g/l succinic acid 0.01mol/l 21.20 g/l NaH₂PO₂ × H₂O  0.2 mol/lComposition of Base Electrolyte 3:

26.29 g/l  NiSO₄ × 6H₂O  (0.1 mol/l) 26.47 g/l  Na₃ citrate × 2H₂O (0.09mol/l) 0.24 g/l Na₂MoO₄ × 2H₂O (0.001 mol/l)  1.18 g/l succinic acid(0.01 mol/l) 31.8 g/l NaH₂PO₂ × H₂O  0.3 mol/lComposition of Base Electrolyte 4:

26.29 g/l NiSO₄ × 6H₂O (0.1 mol/l) 26.47 g/l Na₃ citrate × 2H₂O (0.09mol/l)   0.24 g/l Na₂MoO₄ × 2H₂O (0.001 mol/l)  23.62 g/l succinic acid(0.2 mol/l) 21.20 g/l NaH₂PO₂ × H₂O 0.2 mol/lAddition of Additives:

Additives can also be added to all base electrolytes 1 to 4. To thisend, either

3.75 ppm of dithiodiglycolic acid or

75 ppm of Brij 58

individually or a combination of both is added before the pH is adjustedto 9.0.

Experimental Conditions:

After cleaning and Pd activation, the substrates are dipped into theelectroplating solution (solution is stirred). The mixture is heated to55° C. Autocatalytic deposition is carried out for 2 minutes. As soon asan NiMoP alloy is deposited on Pd nuclei, this becomes visible through alayer with a metallic lustre. After deposition of the alloy, thesubstrate is rinsed with deionised water and carefully blown dry usingnitrogen gas.

EXAMPLE 2 Step 1 Cleaning as Under Example 1 Step 2 (DirectAutocatalytic Deposition without Pd Activation)

For direct electroless deposition of a metallic alloy (NiMoP) on coppersurfaces, no activation via Pd catalyst nuclei takes place in this case.Instead, the NiMoP solution is modified by the addition of DMAB asinitiator and employed for electroless deposition. In order to carry outthe experiments, various borane concentrations in the range 0.004-0.15mol/l are used.

Composition of base electrolyte 1 as described under step 3 withaddition of:

Dimethylaminoborane=0.004 and 0.012 mol/l

Of the individual substances, stock solutions are prepared whoseconcentration is selected in such a way that the solutions are mixed inequal volume ratios and give the respective base electrolyte. To thisend, the substances are dissolved in deionised water in a 1 l volumetricflask.

Stock solution K1=131.5 g/l NiSO₄×6H₂O

Stock solution K2=132.4 g/l Na₃ citrate×2H₂O

Stock solution K3=1.2 g/l Na₂MoO₄×2H₂O (for base electrolyte 1)

Stock solution K4=118.1 g/l succinic acid

Stock solution “K5-1”=106.0 g/l NaH₂PO₂×H₂O+5.88 g/l dimethylaminoborane

Stock solution “K5-2”=106.0 g/l NaH₂PO₂×H₂O+17.69 g/ldimethylaminoborane

After preparation of a mixture of K1-K4 which in each case consists of100 ml of K1, K2, K3 and K4 and has been prepared in accordance with theexperimental plan, 160 ml thereof and 40 ml of K5-1 are introduced intoa beaker. For the experiments with solution K5-2, the mixture of K1-4 isprepared freshly. Again, 120 ml of K1-K4 are taken and 30 ml of K5-2 areadded.

Experimental Conditions:

After cleaning, the substrates are rinsed for 30 seconds with deionisedwater. This is followed by an additional cleaning step in ethanol. Thesubstrates are rinsed for 10 seconds with deionised water andsubsequently dipped into the electroplating solution (solution isstirred). The deposition is carried out for 30 seconds with mixture K5-1at 60° C. and with K5-2 at 50° C. As soon as NiMoP alloy is deposited onPd nuclei, autocatalytic deposition takes place, which becomes visiblethrough a layer with a metallic lustre. After deposition of the alloy,the substrate is rinsed with deionised water and carefully blown dryusing nitrogen gas.

EXAMPLE 3

Determination of selective deposition vis-à-vis various insulatingmaterials with Pd activation solution:

Solu- Temper- tion Substrate ature Time 1 Time 2 Time 3 Time 4 K1- 01 Cu01 55.4° C. 120 sec 30 sec 10 sec 120 sec K5 02 Cu 02 55.4° C. 120 sec30 sec 10 sec 120 sec 03 SiO₂ 01 55.2° C. 120 sec 30 sec 10 sec 120 sec04 SiO₂ 02 55.2° C. 120 sec 30 sec 10 sec 120 sec 05 SiN 01 55.2° C. 120sec 30 sec 10 sec 120 sec 06 SiN 02 55.4° C. 120 sec 30 sec 10 sec 120sec 07 SiOC 01 55.3° C. 120 sec 30 sec 10 sec 130 sec 08 SiOC 02 55.3°C. 120 sec 30 sec 10 sec 120 sec 09 SiC 01 55.4° C. 120 sec 30 sec 10sec 120 sec 10 SiC 02 55.4° C. 120 sec 30 sec 10 sec 120 sec 11 TiN 0155.4° C. 120 sec 30 sec 10 sec 120 sec 12 TiN 02 55.4° C. 120 sec 30 sec10 sec 120 sec 13 TaN 01 55.3° C. 120 sec 30 sec 10 sec 120 sec 14 TaN02 55.3° C. 120 sec 30 sec 10 sec 120 sec Time 1: PCC-350 Time 2:deionised water Time 3: activation Time 4: deposition

For copper substrates K1-K5 01 and O₂, deposition is observed, whereasno deposition on NiMoP takes place for the other substrates K1-K5 03 to14.

EXAMPLE 4

Determination of selective deposition vis-à-vis various insulatingmaterials by direct autocatalytic plating:

Solu- Temper- tion Substrate ature Time 1 Time 2 Time 3 K1-K4 + 25 TaN01 59.3° C. 120 sec 30 sec 120 sec  K5-1 26 TaN 02 59.6° C. 120 sec 30sec 120 sec  15 TiN 01 60.2° C. 120 sec 30 sec 30 sec 16 TiN 02 60.2° C.120 sec 30 sec 30 sec 17 SiO₂ 01 74.6° C. 120 sec 30 sec 30 sec 18 SiO₂02 75.6° C. 120 sec 30 sec 30 sec 19 SiC 01 75.3° C. 120 sec 30 sec 30sec 20 SiC 02 74.4° C. 120 sec 30 sec 30 sec 21 SiN 01 73.5° C. 120 sec30 sec 30 sec 22 SiN 02 72.6° C. 120 sec 30 sec 30 sec 23 SiOC 01 71.7°C. 120 sec 30 sec 30 sec 24 SiOC 02 70.8° C. 120 sec 30 sec 30 sec Time1: PCC-350 Time 2: deionised water Time 3: deposition

Deposition was not observed in any of cases K1-K4+K5-1 15 to 26.

The invention claimed is:
 1. A process for the production of anelectrically conductive structure, comprising: (i) electrolesslydepositing a first layer comprising at least one on at least one of acatalytically activated semiconductor layer and a catalyticallyactivated insulating layer, (ii) depositing a copper interconnect on thefirst layer, and (iii) electrolessly depositing a second layercomprising at least one alloy on the copper interconnect, wherein thefirst layer is a diffusion barrier, and the second layer is anencapsulation barrier, to form an electrically conductive structurecomprising (1) at least one of the catalytically activated semiconductorlayer and the catalytically activated insulating layer, (2) the firstlayer, (3) the copper interconnect, and (4) the second layer, whereinthe first layer and the second layer are adjacent the copperinterconnect, and wherein an alloy in at least one of the first layerand the second layer comprises Mo, Re or W in an amount of from 2 to 25at-% as a refractory metal which increases the thermal stability of thebarrier layer, and wherein during the electroless depositing of thefirst layer a concentration of Mo in an electroless plating solution is3×10⁻² mol/l or less, a concentration of W is 1×10⁻¹ mol/l or less and aconcentration of Re is 1×10⁻¹ mol/l or less.
 2. The process according toclaim 1, wherein the electroless depositing forms at least one of thefirst layer and the second layer which comprise at least one of NiReP,NiMoP, NiWP, NiReB, NiMoB, NiWB, NiRePB, NiMoPB and NiWPB alloys.
 3. Theprocess according to claim 1, wherein, as the refractory metal,molybdenum is present in at least one of the first layer and the secondlayer in an amount of from 3 to 24 at-% or Re in an amount of from 2 to23 at-% or tungsten in an amount of from 5 to 15 at-%.
 4. The processaccording to claim 1, wherein the electroless deposition comprisesdepositing a thin metal-alloy film on a surface of a metal substrate,wherein the electroless deposition is carried out by spraying asemiconductor substrate with an autocatalytic plating solution or dippedinto the autocatalytic solution, causing the electroless deposition of athin metal-alloy film comprising at least one metal selected from thegroup consisting of Ni, Co, Pd, Ag, Rh, Ru, Re, Pt, Sn, Pb, Mo, W andCr.
 5. The process according to claim 4, wherein the metal substrateconsists of a metal selected from the group consisting of Cu, Ag, Co,Ni, Pd and Pt.
 6. The process according to claim 4, wherein theautocatalytic plating solution is essentially free from surface-activesubstances.
 7. The process according to claim 4, wherein theautocatalytic plating solution comprises at least one surface-activesubstance and optionally at least one additive for improving the layerproperties and nature of one of the first layer and the second layer. 8.The process according to claim 4, wherein the autocatalytic platingsolution comprises one or more stabilisers for extending the bathservice lives of the electroplating solutions.
 9. The process accordingto claim 4, further comprising cleaning and activating one or moresurfaces of the copper interconnect with ammonia- and hydrofluoricacid-free solutions.
 10. The process according to claim 1, wherein theelectroless depositing forms a first layer comprising at least one alloyselected from the group consisting of NiReP, NiReB, NiMoB, NiMoP, NiWB,NiRePB, NiMoPB and NiWPB.
 11. The process according to claim 1, whereinthe electroless depositing forms a second layer comprising at least onealloy selected from the group consisting of NiReP, NiReB, NiMoB, NiWB,NiMoP, NiRePB, NiMoPB and NiWPB.
 12. A process for the production of anelectrically conductive structure, comprising: (i) electrolesslydepositing a first layer comprising at least one alloy selected from thegroup consisting of NiRePB, NiMoPB and NiWPB on at least one of acatalytically activated semiconductor layer and a catalyticallyactivated insulating layer, (ii) depositing a copper interconnect on thefirst layer, and wherein the first layer is a diffusion barrier, to forman electrically conductive structure comprising (1) at least one of thecatalytically activated semiconductor layer and the catalyticallyactivated insulating layer, (2) the first layer, and (3) the copperinterconnect, wherein the first layer is adjacent the copperinterconnect.
 13. The process of claim 12, wherein the alloy comprisesat least one of Mo, Re and W in an amount of from 2 to 25 at-%.
 14. Theprocess according to claim 12, wherein the first layer comprises from 3to 24 at-% of Re.
 15. The process according to claim 12, wherein thefirst layer comprises Mo in an amount of from 3 to 24 at-%.
 16. Theprocess according to claim 12, wherein the first layer comprises W in anamount of from 5 to 15 at-%.
 17. A process for the production of anelectrically conductive structure, comprising: (i) cleaning and/oractivating a copper interconnect with at least one of chemicalmechanical planarization, an ammonia-free solution and a hydrofluoricacid-free solution, and (ii) electrolessly depositing an encapsulationlayer on the cleaned and/or activate copper interconnect, wherein theencapsulation layer comprises at least one alloy selected from the groupconsisting of NiRePB, NiMoPB and NiWPB, to form an electricallyconductive structure wherein the encapsulation layer is adjacent thecopper interconnect.
 18. The process of claim 17, wherein the alloycomprises at least one of Mo, Re and W in an amount of from 2 to 25at-%.
 19. The process according to claim 17, wherein the encapsulationlayer comprises Mo in an amount of from 3 to 24 at-%.
 20. The processaccording to claim 17, wherein the encapsulation layer comprises Re inan amount of from 2 to 23 at-%.
 21. The process according to claim 17,wherein the encapsulation layer comprises W in an amount of from 5 to 15at-%.